Need to export animations into FBX without interpolations (need just keys solely )
I seem to find out this time values order - while exporting constantly interpolated animation every framekey is presented as a pair, the first one's tick is -1 by number then the actual frame's tick in dope sheet and it contains the translation and rotation BEFORE the actual frame tick value, while the second data in this framekyes pair shows actual trnslation and rotation at the actual time in dope shit, to clarify:
3 actual framekeys with constant interpolation:
Assimp gives 6 stored keys, first couple is, lets say, 8th tick first  and 9th tick second, this first keys means BEFORE 8th time value all previous ticks the model has translation and rotation it contains. The second one, that shows 9th tick is actual framekey change...Following this the next pair will contain, lets say, 18th and 19th time ticks, and that means that between 9th and 18th tick the bone had stable translation and rotation while at the 19th tick its going to change again. Every second framekey data will repeat every first framekey data in the next couple - this is just an interval where bones were not transfromed because of constant interpolation. Every second is actual translation/rotation of the bone. Just in case someone faces the same strange at first sight Assimp FBX loader behavior :)